1. Field of the Invention
The present invention relates to vehicle exhaust systems and noise cancelling devices therefor. More specifically, the present invention is related to vehicle exhaust drone reducing assembly that attenuates or cancels target frequencies that cause audible droning in the system without restricting the flow of exhaust gas for performance vehicles.
Vehicle exhaust systems are designed to evacuate exhaust gases from the engine after combustion, whereby the exhaust gases are rapidly withdrawn from the engine combustion chamber, into the exhaust manifold and through the exhaust system to the atmosphere. To maintain peak performance of an engine, the flow of air through the engine must flow freely through the system and not be hampered by high pressure areas or physical blockages. This includes excessive backpressure on the exhaust system, which stifles the flow of exhaust gas exiting the engine.
Most modern cars include complicated exhaust systems comprised of catalytic converters, advanced muffler systems, particulate traps, and other assemblies within the system that reduce the otherwise free flow of air. While these devices reduce harmful emissions, they create encumbrances on the system that reduce its efficiency. To improve engine performance for the high performance vehicles, these exhaust systems are optimized for efficient air flow so as to eliminate as much back pressure as possible so that engine performance can be maximized.
However, a drawback associated with many aftermarket, non-OEM exhaust systems is that they tend to be less developed than most factory or original equipment systems, and therefore tend to include unwanted effects such as increased noise production. One common type of audible effect known in the art is exhaust “drone”, in which the exhaust system emits a high amplitude, low frequency tone that is not pleasing to the ear and can be a nuisance to the driver and others. Drone is a result of the moving exhaust gases interacting with the exhaust system components, wherein one or more components experience an excitation in close proximity to a system or component resonant frequency. This in turn creates a steady, high amplitude noise at certain engine speeds, which can be pervasive in the vehicle interior and particularly loud outside of the vehicle.
The drone created by most exhaust systems is a nuisance for the vehicle occupants, particularly over long trips, as well as to nearby pedestrians. Moreover, the vibrations that cause the drone and can create turbulence in the exhaust gases within the system, thereby increasing backpressure, reducing horsepower and interfering with optimal engine performance across its speed range. It is well known that exhaust drone is a byproduct of the vehicle exhaust components, including their size, weight, and positioning. It is also a byproduct of the connection between the vehicle and the system itself. The exhaust system components include, inter alia, catalytic converters, resonators, mufflers, exhaust tips, lengths of exhaust tubing, hangers and other coupling components. All of these individual parts collectively and individually have a frequency at which they will resonate. The frequency of engine cycling through its stages and the excitation energy of the pulses generated thereby contribute to exhaust drone, which can range from tolerable to very intense, depending upon the setup.
Yet another cause of exhaust drone is unequal exhaust tubing length for dual exhaust vehicles. Unequal exhaust tubing means that exhaust gases traversing the system travel in one of two paths, wherein one path is longer than the other. This leads to complex frequencies that are difficult to counteract and attenuate. Unfortunately, the drone range for most vehicle exhaust systems is generally within the ranges of normal city and highway driving, therefore the prevalence of exhaust drone is common in aftermarket systems, and countering the noise can be quite difficult.
The present invention relates to an energy attenuation system that is adapted to connect between the two runs of an exhaust system and connect to two points therealong. The system absorbs excitation energy between the exhaust runs and creates an anti-phase vibration that effectively cancels the vibration and thus the audible signal generated by the system. By contrast to most existing systems, which utilize active noise cancelling, the present invention is a structure attached to the exhaust system for canceling the noise source without requiring electrical power. The structure is tuned for a specific range of frequencies and operates as a passive noise attenuation device without adding speakers or resonators to the system.
2. Description of the Prior Art
Devices have been disclosed in the prior art that relate to noise cancelling systems. These include devices that have been patented and published in patent application publications, and generally relate to active noise control systems that utilize speaker systems drawing electrical power to cancel drone and other unwanted noise. The following is a list of devices deemed most relevant to the present disclosure, which are herein described for the purposes of highlighting and differentiating the unique aspects of the present invention, and further highlighting the drawbacks existing in the prior art.
Solutions in the art include both passive and active sound cancelling solutions. Passive solutions include resonators and specifically designed structures that do not have overlapping resonant frequencies. Active sound cancelling includes audio systems that can react to the unwanted sound and project an anti-phase noise source to cancel out the unwanted sound. These solutions are effective at attenuating or preventing exhaust noise in the art, however these add weight and complexity to the vehicle exhaust system, as well as significant costs.
Active noise cancelling systems in the art include those that employ speakers or other noise generators in the exhaust system to project anti-phase sound to cancel out the unwanted noise. Solutions such as these exist in the art. Examples include U.S. Pat. No. 5,541,373 to Cheng and U.S. Pat. No. 5,229,556 to Geddes. Both of these devices employ an active exhaust silencer, wherein a chamber is provided having one or more speakers for actively cancelling out a noise frequency in the exhaust system. U.S. Pat. No. 5,619,020 to Jones is another device in the art, which discloses an active noise cancelling assembly that is disposed within the muffler of a vehicle and includes loudspeakers injecting anti-noise thereinto.
These systems are effective for cancelling noise sources within an exhaust system, however they require sophisticated electronics and fragile components to operate effectively. These include loudspeakers and supporting electronics, as well as microphones in some instances to monitor the exhaust noises and change the anti-phase noise to cancel the same. Such systems are expensive and prone to failure over long durations. The present invention, by contrast, is a passive noise cancelling system that utilizes physical structure to attenuate frequencies in the exhaust and change is sound qualities for the purposes of cancelling unwanted drone.
Specifically, the present invention contemplates an assembly suitable for use with an exhaust system having dual exhaust outlets from the vehicle engine, regardless of whether the rear of the vehicle has a dual exhaust outlet or a rejoined, single outlet. The assembly is placed between two exhaust paths and connected therebetween such that vibration of the system is neutralized by tuning the structure of the present invention to attenuate dominate frequencies in the exhaust. The assembly comprises a series of tuning rods disposed between end plates and connected to portions of the exhaust pipe at its ends, wherein the tuning rods are stiffened such that the resonate frequency thereof and of the system offsets the drone frequency of the exhaust system. The compression within the rods changes their stiffness and thus the frequency response thereof, thereby changing the modes of the assembly. The system can be setup such that these modes are anti-phase to the exhaust modes, thereby attenuating the drone emanating therefrom.
It is submitted that the present invention improves the art of passive noise cancelling solutions in the art. Current methods of addressing drone using a passive noise cancelling means include attaching different types and styles of resonators to the system, using specific muffler designs, attaching resonating exhaust tips to the ends of the exhaust system, and further employing various methods that adjust the weight of the system in critical locations, whereby changing the exhaust system characteristics. These existing methods often improve exhaust drone to some degree, but also change the tone and “character” of the vehicles exhaust. Some of these methods, such as replacing the muffler, can negatively impact a cars performance. The present invention provides a solution for vehicle exhaust systems, whereby the flow of exhaust gases is not changed and the anti-phase frequency can be “dialed-in” for specific exhaust systems.
The present invention diverges in design elements and structure from the prior art, and consequently fulfills a need in the art for improved passive noise cancelling means within an exhaust system. The present invention fulfills this need without the drawbacks of the prior art, which include more complex systems and those that potentially interfere with the operation of the exhaust or change its sound qualities while attempting to remove drone modes.